The molecular machinery inside a chloroplast
How to pack many photosynthesis enzymes in a small area
Utrecht scientists uncovered the molecular machinery inside the chloroplasts of plants, paving the way for research on protein interactions on cell surfaces. They publish their findings in Nature Communications.
Plants can thrive in ever-changing environmental conditions, due to highly efficient machinery to catalyze the oxidation of water through the so calledPhotosystem II enzyme coupled to a modular antenna system (LHCII). To pack as many of these molecular machines as possible in the highly folded thylakoid membranes of the chloroplast, plants take advantage of interactions between different copies of LHCII proteins ultimately constructing so-called grana.
So far, this process was poorly understood, but researchers at Utrecht 木瓜福利影视 in collaboration with researchers from the Politecnico di Torino have managed to prove the structural role of PSII-LHCII complexes in this process for the first time. Understanding these structural interactions in detail helps researchers to understand how grana are formed and dynamically adjusted 鈥 the process by which plants regulate membrane structure and thus, ultimately, efficiently harvest sunlight. They published their results in the respected scientific journal Nature Communications.
Structural biology
To unravel the interactions leading to the formation of grana two separate mass spectrometry techniques were applied 鈥 top-down mass spectrometry to characterize all proteins in the complex and cross-linking mass spectrometry to detect which proteins are interacting. Even though mass spectrometry is a technique that essential weighs molecules, such information can readily be extracted from the sample.
The ability of structural proteomics to uncover these interactions inside the membrane, opens the way for application to disease models.
鈥淔rom the analyses, the post translational modification (PTM) acetylation was found on the start of almost all the protein sequences and additionally many proteins were identified where the first part of the protein sequence was removed鈥, last author Richard Scheltema says. 鈥淭he structural investigation uncovered which proteins are interacting and with which portion of the protein sequence.
A unique mechanism
Using the results from the two mass spectrometry approaches to interpret existing cryo-EM data completely resolved the interactions. 鈥淥ur study confirms a previously suspected connection point between the individual copies and, importantly, found a unique mechanism whereby the interaction is regulated鈥, Scheltema says. 鈥淭he acetylation combined with the processing of the start of the protein sequence, particularly in low light conditions, allows plants to rapidly unlock the interactions between facing complexes by removing the positive charged first amino acid repelling the complex away from the negatively charged stromal surface of the other complex.鈥
Native interactions
In this work the researchers have managed to reproduce their findings on protein complexes still embedded in the folded grana, opening the way for research on protein interactions on surface exposed protein complexes in different organisms. The ability of cross-linking-mass spectrometry to do so has strong implications on understanding protein regulations leading to debilitating diseases in their native environment.
Publication
. Nature Communications, 13 March 2020. Pascal Albanese*, Sem Tamara*, Guido Sarocco, Cristina Pagliano, and Richard A. Scheltema*
* Affiliated with Utrecht 木瓜福利影视
